If you can detect *ANY* voltage AT ALL between chassis ground and the 'ground' at the binnacle or any other ground wires for that matter then you _still_ have a floating ground line (in other words they aren't connected to ground at all).
Testing continuity on this wire *will not* help since your tester is just measuring a path to earth through some other device.
As I said before, the only to find out whether the binnacle wire: a)is a ground wire and b) if it's actually connected, is to trace this wire *by hand*, continuity testing is not going to help.
It's a pain in the arse, but a lot quicker than poking and prodding ad infinitum.
Rich H